The present invention relates to a hydraulic brake booster which provides a power assist during a brake application. The hydraulic brake booster includes a housing which communicates with a pressure source such as a power steering pump. A control valve within the housing is operable to control the communication of fluid pressure through the housing. In order to operate the control valve, an input member extends into the housing and is movable during a brake application to impart movement to the control valve. Movement of the control valve communicates fluid pressure to a pressure chamber wherein an output member is movable in response to the fluid pressure to effect a power-assisted brake application.
A hydraulic brake booster such as is illustrated in U.S. Pat. Nos. 3,831,491 and 3,995,529 utilizes an input member to develop fluid pressure within a control chamber. The fluid pressure in the control chamber is communicated to a control valve which moves in response thereto and communicates fluid pressure from a pressure source to a working chamber to bias an output member to a braking position. The control chamber is disposed on the front or input member side of the output member so that the hydraulic brake booster housing must be extended where the input member is located to accommodate the input member and control chamber. This extension of the housing is not acceptable with the smaller more efficient vehicles because of the space limitations within an engine compartment.
The present invention overcomes these space limitations by disposing the control chamber on the side of the booster housing defining an opening for receiving the output member. In addition, the input member extends through a working chamber or first pressure chamber and is exposed to the control chamber or second pressure chamber. The input member is movable within the housing to develop fluid pressure within the second pressure chamber and communicate the fluid pressure to the control valve, whereupon the control valve moves to communicate fluid pressure with the first pressure chamber. The fluid pressure within the first pressure chamber acts against the input member to bias the same toward the second pressure chamber to increase the fluid pressure therein so as to bias the output member to move to actuate braking.
In a preferred embodiment, the housing defines a small diameter bore, a large diameter bore and an intermediate diameter bore. The input member sealingly and movably engages the small diameter bore and the large diameter bore while the output member sealingly and movably engages the intermediate diameter bore.
An advantageous effect of the invention follows that the hydraulic brake booster housing can be made smaller as the control chamber is disposed within an existing portion of the stepped bore rather than requiring an extension of the housing to accommodate the control chamber on the side of the housing supporting the input member.